Methods for Repairing a Workpiece

ABSTRACT

A method for repairing a workpiece includes the steps of providing an unstripped, coated workpiece comprising a surface having a localized damage site; masking the workpiece about the localized damage site; generating a microplasma stream; and applying a first powdered material to the localized damage site using the microplasma stream; and applying a second powdered material to the workpiece surface using the microplasma stream. Another method for repairing a workpiece includes the steps of providing an unstripped, coated workpiece comprising a surface having a localized damage site; generating a microplasma stream; applying without a maskant a powdered metal alloy to the damage site using the microplasma stream; and dimensionally restoring the workpiece.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 11/253,868, filed Oct. 19,2005, and entitled METHODS FOR REPAIRING A WORKPIECE, and this is acontinuation-in-part of Ser. No. 10/982,041, filed Nov. 4, 2004, andentitled PLASMA SPRAY APPARATUS, the disclosures of which areincorporated by reference herein in their entirety as if set forth atlength.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to a method for repairing aworkpiece, and more particularly, a method for repairing a workpieceusing a microplasma spray coating.

BACKGROUND OF THE DISCLOSURE

Generally, conventional plasma spray coating apparatus are imprecise inapplying their plasma spray coatings due to the size and width of theplasma stream. The plasma spray coating process typically requires theworkpiece to be masked in areas where the material transfer is notdesired and/or not required. Conventional plasma spray coating methodsand apparatus require masking the workpiece and applying the coating dueto the plasma spray coating pattern being too wide to accurately controlthe coating process. Such operating conditions inhibit and/or renderdifficult the ability to spot coat workpieces in order to form a depositand replace or augment parent material.

Consequently, there exists a need for a method for repairing a workpieceusing a microplasma spray coating capable of being applied as a spotcoating without the need for masking while still providing acceptablespray coating quality.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method for repairing aworkpiece broadly comprises providing an unstripped, coated workpiecebroadly comprising a surface having a localized damage site; masking theworkpiece about the localized damage site; generating a microplasmastream; applying a first powdered material to the localized damage siteusing the microplasma stream; and applying a second powdered material tothe workpiece surface using the microplasma stream.

In accordance with the present invention, a method for repairing anunstripped, coated workpiece broadly comprises providing a workpiececomprising a surface having a localized damage site; generating amicroplasma stream; applying without a maskant a powdered metal alloy tothe localized damage site using the microplasma stream; anddimensionally restoring the workpiece.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a microplasma spray gun and a workpiece;

FIG. 2 is a partially exploded view of a microplasma spray apparatus;

FIG. 3 is a view of the microplasma spray apparatus of FIG. 2 applying amaterial to a workpiece; and

FIG. 4 is a flowchart of a process applying the material.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

In performing the method(s) described herein, it is contemplated that astationary microplasma spray coating apparatus, automated microplasmaspray coating apparatus, remote controlled microplasma spray coatingapparatus, robotic or robot implemented microplasma spray coatingapparatus, and portable microplasma spray coating apparatus may beutilized. The stationary, automated, remote controlled and roboticimplemented models are typically utilized within an enclosure such as adedicated room where the ultra violet light level may be controlled andexcess microplasma spray and/or powdered material may be collected withease. It is also contemplated that a portable microplasma spray coatingapparatus may be mounted on a mobile platform such as a vehicle, andtransported to on-site locations to quickly facilitate repair work. Sucha portable microplasma spray coating apparatus is described in U.S.patent application Ser. No. 11/190,135, Attorney Docket No. 05-199,assigned to United Technologies Corporation, the assignee of recordherein, which is incorporated herein by reference as if set forth atlength.

FIG. 1 shows a microplasma spray apparatus 10. The exemplary microplasmaspray apparatus 10 includes a microplasma gun 12 having an arc gasemitter 14, an anode 16, and a cathode 18. An electric arc 20 isgenerated between the anode 16 and cathode 18. A plasma stream 21 isformed when arc gas is injected from the arc gas emitter 14 through thearc 20. A powdered material injector 22 dispenses powdered material intothe plasma gas stream, which transports the powdered material to theworkpiece 24. As a result, the powdered material forms a deposit on adesired location on the workpiece 24.

FIGS. 2 and 3 show further details of one exemplary microplasma sprayapparatus 10. The apparatus 10 may be operable for depositing materialon many things, including, but not limited to at least a portion of ablade 72 in a gas turbine engine (not shown).

In the exemplary embodiment, the cathode 18 is held within and extendingfrom an insulated body 26 of a cathode cartridge or assembly 28. Theexemplary cartridge 28 also includes threads 30 for threadingly engagingthe microplasma gun body. The exemplary cathode 18 also includes anO-ring seal 32 to seal the leak path that is created at the interfacebetween the cartridge 28 and the microplasma gun body.

In operation, an electric arc 20 (FIG. 1) is generated between the anode16 and cathode 18. Arc gas such as, but not limited to, argon is emittedinto the electric arc 20. The arc gas can be emitted prior to generatingthe electric arc. The electric arc ionizes the gas to create the plasmagas stream 21. The ionization process removes electrons from the arcgas, causing the arc gas to become temporarily unstable. The arc gasheats up to approximately 20,000°-30,000° F. as it re-stabilizes. Theplasma stream cools rapidly after passing through the electric arc.

A powdered material injector 22 injects powdered material 34 into theplasma gas stream 21. The powdered material 34 is heated to asuper-plastic state in the plasma stream and is deposited on the blade(FIG. 3) where it cools and re-solidifies to form the deposit. Theexemplary powdered material injector 22 includes a powder hopper 36 forholding the powdered material 34. The exemplary hopper 36 is attached tothe microplasma gun 12 via a connector 38 formed on the microplasma gun12. The powdered material 34 is channeled through a discharge tube 40and controlled by a valve 42 positioned in the discharge tube 40. Thevalve 42 can be mechanical or electromechanical as is known to thoseskilled in the art. There may be multiple hoppers (e.g., to containmultiple components mixed at discharge/injection. Powder mayalternatively be injected into the plasma stream via one or more powdergas lines from one or more remote powder feeders (not shown).

A nozzle shroud 46 positioned on a forward wall 48 of the microplasmagun 12 holds a nozzle insert 50 and permits the electrode 28 to extendthrough a center aperture 52 formed in the nozzle shroud 46. The nozzleinsert 50 can be threadingly attached to an end of the nozzle shroud 46.A shield gas cap 54 is positioned adjacent the nozzle shroud 46. Aninsulator 56 is positioned between the shield gas cap 54 and the nozzleshroud 46 to electrically isolate the shield gas cap 54 from the nozzleshroud 46. The shield gas cap 54 can be pressed to fit onto the nozzleshroud 46 and over the insulator 56. The shield gas cap 54 includes aplurality of through apertures 58 for permitting shield gas to flowtherethrough and shield the arc gas from ambient atmosphere. A centeraperture 60 formed in the shield gas cap 54 permits high velocity arcgas to pass through and into the electric arc.

Cooling fluid, such as water or the like, may be utilized to cool themicroplasma gun 12. The cooling fluid is delivered to the microplasmagun 12 via a cooling fluid hose 62. The cooling fluid traverses throughinternal passages (not shown) in the microplasma gun 12 and flowsthrough an inlet passage 64, into an anode holder 66 and back through anoutlet passage 68. The cooling fluid reduces the temperature of theanode 16 during operation of the microplasma gun 12. The cooling flowrate may be approximately 0.1 to 1 gallons per minute. A second conduit70 is connected to the microplasma gun 12. The second conduit may beoperable for providing electrical power, arc gas, and shield gas to themicroplasma gun 12.

The microplasma gun 12 may be operated at a relatively low power rangeof between approximately 0.5 Kilowatts and 4 Kilowatts. The low poweroutput of the microplasma gun 12 significantly reduces the heat flowinto the blade 72 over that of conventional coating methods. The maximumsurface temperature of the blade 72 caused by the coating process isapproximately 200° F. depending on the mass of the blade. Themicroplasma gun 12 is operable for applying powdered material 34 to athin wall area of the blade 72 without distorting the blade 72 becausethe low power output limits the localized stress caused by high thermalgradients.

The powder hopper 36 holds the powdered material 34 prior to beinginjected into the plasma gas stream 21 by the powder injector 22. Thepowdered material 34 can be injected into the plasma gas stream 21either through gravity feed or through a pressurized system (not shown).The shut-off control valve 42 controls the powdered material 34 feedrate into the plasma gas stream 21. Powdered material 34 is transferredto the blade 72 at an approximately 1 to 30 grams per minute. Whenemploying a pressurized system, the powder gas flow may be atapproximately 0.1 to 1.5 liters per minute. Generally, the microplasmagun 12 may be positioned from a component to be coated at a distance ofapproximately 1.5 inches (3.8 centimeters) to 8 inches (20 centimeters).The microplasma gun 12 may apply the material from exemplary distancesof approximately 2.5 inches (6.4 centimeters) to 6.5 inches (16.5centimeters) to the blade 72, or other components, but can varydepending on the coating application requirements. The exemplarymicroplasma spray gun 12 can be oriented between a positive 45° angleand a negative 45° angle relative to a normal axis of the blade andstill provide adequate material delivery with a gravity feed system. Apressure feed system may provide greater orientational freedom for themicroplasma gun 12. The microplasma spray gun 12 advantageouslygenerates a relatively low noise level that ranges (e.g., 40-70 dB) dueto the low power output, thereby making the apparatus 10 suitable forhand held application. Current U.S. government regulations requirehearing protection when environmental noise reaches 85 dB. Themicroplasma spray apparatus 10 can be hand held or alternatively held inan automated fixture (not shown) that is computer controlled.

FIG. 4 shows the operation of the microplasma spray apparatus 10.Initially, at block 80, arc gas is emitted from the nozzle insert 50. Anelectric potential is generated between the anode 16 and the cathode 18of the plasma spray gun 12 and is directed through the arc gas, asdescribed in block 82. Arc gas is directed through the electricpotential to create the plasma stream 21. At block 84, powdered material34 is injected into the plasma stream 21. At block 86, the plasma streamheats the powdered material 34 to a “super plastic” condition such thatthe powdered material 34 is malleable when it is applied to a workpiece.At block 88, the powdered material 34 is applied to an unmaskedsubstrate. The powdered material 34 then bonds with the substrate andcools to form a solid deposit on the substrate. Optionally, prior toapplying the powdered material 34, the surface of the unmasked substratemay be roughened to improve the adhesive properties of the substratesurface to receive the powdered material 34. The substrate surface maybe roughened using mechanical techniques (e.g., grit blasting),thermionic cleaning, or combinations using such techniques, and thelike, as known to one of ordinary skill in the art, and then cleaned toremove contaminants and excess remnants of the roughening processes.

The microplasma gun 12 can apply the material in small spots (e.g.,about 1 millimeter to about 5 millimeters in diameter) or apply a streamof material in a sweeping motion to form narrow strips (e.g., about 0.5millimeters to about 5 millimeters in width). For purposes of theintended application, the microplasma gun preferably applies material insmall spots to repair coating chips. This permits accurate surfacecoating even with a hand held device. The small spot/strip size maysubstantially eliminate the need for masking or otherwise covering theblade 72 in areas where the material is unwanted. The nozzle openingsize controls the spray pattern. The hand-held version of themicroplasma gun 12 may be sufficiently accurate that material can besprayed on components while they remain installed in an engine or thelike.

An exemplary arc gas flow rate of the microplasma apparatus 10 may beabout 0.5 to about 3 liters per minute. As stated above, the arc gas andshield gas are typically argon, but any suitable inert gas can beutilized. An exemplary shield gas flow rate ranges may be about 2 toabout 8 liters per minute for a typical application.

For purposes of illustration, and not to be taken in a limiting sense,the methods for repairing workpieces contemplated herein will bedescribed with respect to using the aforementioned portable, hand-heldmicroplasma spray coating apparatus. It is contemplated as will berecognized by one of ordinary skill in the art that the aforementionedportable, hand-held microplasma apparatus may be outfitted for use inthe aforementioned stationary, automated, remote controlled and roboticimplemented models. It is contemplated that the workpieces may comprisevarious gas turbine engine and turbomachinery components related, butnot limited to, a fan, turbine, compressor, vane, blade, casing,combustion chamber, combustor panel, seals, rings, and the like, as wellas other similar components in other industrial applications.

As used herein, the term “coated workpiece” means a turbine enginecomponent having at least one layer of coating covering the entiresurface or substantially the entire surface of the part. As used herein,the term “unstripped, coated workpiece” means a coated workpiece whosecoating layer(s) have not been stripped off or removed to expose theworkpiece surface or intermediate layers of coating. As used herein, theterm “localized damage site” represents an exposed portion of anintermediate layer of coating and/or the workpiece surface. As usedherein, the term “unstripped, coated workpiece having a localized damagesite” means a coated workpiece having a localized damage site surroundedby the remaining coating layers.

FIG. 3 shows a coated workpiece having a localized damage site, forexample, the blade 72 having a localized damage site 73 along an airfoil74. Such a damage site 73 or other localized area may receive a depositof the powdered material 34. The plasma gas stream 21 is directed towardthe damage site 73. The site may be a raw damage site or a treated site(e.g., where further material has been machined from the blade substratesuch as to remove contaminants) such as a spot or a chip, or requiredimensional restoration.

The powdered material may be provided as a single powder of a singlealloy as a mechanical blend or multiple alloys either pre-mixed or mixedby the apparatus. The component powders may be selected in view of theworkpiece properties. The workpiece may comprise a nickel-based alloy, acobalt-based alloy, a ferrous-based alloy such as steel, atitanium-based alloy, an aluminum-based alloy, and combinations thereof.The apparatus may be used to form a deposit for replacing parentmaterial lost from the substrate (e.g., due to damage plus cleaning andpreparation) or to augment (e.g., fill a manufacturing defect, coat witha dissimilar material, or otherwise).

The workpiece may comprise any component used in operating conditionswhere a protective coating is necessary to withstand, for example,burn-through, diffusion-controlled deformation (“creep”), cyclic loadingand unloading (“fatigue”), chemical attack by hot gas flow(“oxidation”), wear from contact with other parts, wear from the impactof particles entrained in the gas flow (“erosion”), foreign objectdamage (“FOD”), dimensional restoration, and the like. For purposes ofillustration, and not to be taken in a limiting sense, the workpiece maybe a gas turbine engine blade. In addition, the workpiece may compriseany of the aforementioned gas turbine engine and turbomachinerycomponents. Gas turbine engine components and associated hot sectionhardware are typically coated with a metallic coat alone or a metallicbond coat and a ceramic top coat. Accordingly, the aforementioned gasturbine engine components may have dimensions restored with variousmetallic coatings.

The metallic bond coat may comprise any suitable bond coat known in theart. For example, the bond coat may be formed from an aluminumcontaining material, e.g., nickel aluminum; an aluminide, e.g., aplatinum aluminide; or an MCrAlY material where M includes, but is notlimited to, nickel, cobalt, or other alloys, which are well known in theart. The ceramic top coat may comprise a thermal barrier coatingcomprising, for example, yttria stabilized zirconia. Representativethermal barrier coatings may include, but are not limited to, thosedescribed in, for example, U.S. Pat. No. 4,861,618 to Vine et al.,assigned to United Technologies Corporation, and incorporated byreferenced herein as if set forth at length.

The metallic bond coat may be applied to the damage site 73. Suchprecise spot or chip repair is possible due to the narrow microplasmastream being generated. The metallic bond coat material adheres to theworkpiece substrate material. A maskant or masking agent in minimalamounts is commonly utilized to prevent the area surrounding the damagesite 73 from receiving additional metallic bond coat material. Theceramic top coat may then be applied as a full ceramic coat, that is,applied on the damage site 73 and the entirety of the surface of theblade 72. The added materials strengthen the area under repair bysubstantially reinforcing the eroded/machined repair surface. Forexample, the coating may serve to provide wear resistance to the damagedsite. The repair site, when fully processed (e.g., by heat treatmentprocessing) has properties approaching those of the original coatedparent part surface.

While the methods have been described with respect to spot repair ofthermal barrier coatings on various components, the methods also applyto spot repairs of various single layer metallic coatings fordimensional restoration of gas turbine engine and combustion chambercomponents such as fans, compressors, turbine casings, seals, plates,rings and the like. This dimensional restoration method provides anopportunity to repair a local area without having to strip the entirecoating from the part and recoat the part's entire surface.

Microplasma spray may be used for the dimensional restoration or “chiprepair” of various single layer metallic coatings upon theaforementioned components. The powdered material for use in themicroplasma spray may comprise a metal alloy. Suitable metal alloys fordimensional restoration include, but are not limited to,nickel-aluminum, nickel-chromium (e.g., Inconel 718), nickelchromium-aluminum, molybdenum, aluminum-silicon, and the like. Suitablematerials for wear resistance, e.g., in chip repair, include, but arenot limited to, the carbides of such suitable metal alloys fordimensional restoration. All of the aforementioned metal alloys areoften used for the dimensional restoration of components comprising awide variety of nickel-base alloy, steels, cobalt-base alloy,titanium-base alloy and aluminum-base alloy components, respectively.

This spot application may permit a localized repair of the coatingwithout having to strip the entire coating from the part and re-coat.For example, a spot application of nickel-chrome-chromium carbide, whichis used for high temperature wear resistance on various seals, plates,and rings, may similarly reduce the need to remove previously appliedcoating from the entire part and re-coat.

Using a microplasma stream as described, the powdered metal alloy may beapplied as a single layer metallic coating to the damage site 73. Suchprecise spot or chip repair is possible due to the narrow microplasmastream being generated. The powdered metal alloy adheres to thesubstrate material. Optionally, a maskant or masking agent in minimalamounts may be utilized to prevent the area surrounding the damage site73 from receiving excess powdered metal alloy. The added materialsstrengthen the area under repair by substantially reinforcing theeroded/machined repair surface and providing dimensional restoration.The repair site, when fully processed (e.g., by heat treatmentprocessing) has properties approaching those of the original coatedparent part surface.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible to modification of form, size, arrangement of parts, anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

1. A method for repairing a workpiece, comprising: providing anunstripped, coated workpiece comprising a surface having a localizeddamage site; generating a microplasma stream; applying without a maskanta powdered metal alloy to said localized damage site using saidmicroplasma stream; and dimensionally restoring said workpiece.
 2. Themethod of claim 1, wherein said powdered metal alloy is selected fromthe group consisting of nickel-aluminum, nickel-chromium, nickelchromium-aluminum, molybdenum and aluminum-silicon.
 3. The method ofclaim 1, wherein said powdered metal alloy is nickel-chrome-chromiumcarbide.
 4. The method of claim 1, wherein said workpiece is selectedfrom the group consisting of fans, compressors, turbine casings, seals,plates, rings.
 5. The method of claim 1, wherein said workpiece is a gasturbine engine component.
 6. The method of claim 1, wherein saidworkpiece is a combustion chamber component.
 7. The method of claim 1,wherein said localized damage site comprises a spot or a chip.